I just added a bantam hen to my flock (and rooster). She is not very big even for a bantam but she is sitting in one of the nest boxes continuously. She came from a large flock of bantams. Is it possible that she was sitting on a shared nest there? I had guinea's that several laid their eggs in one hen's nest. When the hen gave up she had been sitting on 37 eggs. I think she got chased off several times by foxes in the area I lived in back in California. This little hen just may have been one of several sitting and or laying eggs in one nest. There were 4 nest boxes for maybe 30 bantams. There was one hen sitting on one of the nests. They had one hen taking care of maybe 15 or 20 chicks in a crate. It was total pandemonium but they all appeared healthy.